Recently, there has been an increase in the number of people who enjoy using high performance personal light boats, for example, personal non-powered boats that are manually propelled by paddling. In particular, kayaks, which are designed to be used in strong currents or on white water rapids, are a traditional type of boat used in extreme water sports that are popular with young adventure and thrill seekers. Furthermore, even if not used in strong currents or on white water rapids, kayaks or canoes can be used as personal water leisure means that enable a user to move far into a calm river or lake or across bodies of water and enjoy fishing or hunting.
Typically, conventional personal small non-poweredboats such as kayaks or canoes are made of thermoformed plastics or glass fiber reinforced plastics (FRP) to form hard hulls or are manufactured by integrally fitting panels made of a hard material such as wood or plywood. Therefore, conventional boats are advantageous in that their safety (durability, water resistance, impact resistance) in water, the strength, and use convenience (control performance, directivity, speed, etc.) resulting from the high stability are excellent. However, such a conventional boat is problematic in that the boat is heavy and production cost thereof is high. In addition, even though the boat is satisfactorily designed such that it can be effectively operated on water, it is difficult to transport the boat to water and store it when not used because of a large size.
Technical efforts to overcome the above problems are classified into the following three categories.
First, as a representative effort that has been widely used before, a boat having a separable structure was proposed. In detail, a frame of a kayak or canoe body includes a plurality of elements (boards, wires, etc. made of wood, metal or synthetic resin or the like) that can be separably assembled with each other by fasteners or connectors. Furthermore, a separate flexible waterproof hull covers the assembled frame. Such a structure for boats is called a skin on frame structure.
Conventional techniques pertaining to this category were in U.S. Pat. Nos. 4,274,170, 4,702,193, 4,841,899, 5,680,828, 5,964,964, and 6,367,405.
Such conventional personal boats pertaining to the first category include a hull that is made of flexible waterproof material and is removably coupled to a separably assembled frame to cover the frame. Thus, compared to traditional integrated boats, these conventional personal boats are advantageous in that transportation and storage thereof are facilitated. However, in the case of most of these conventional personal boats, the number and kind of elements constituting a frame are excessively increased, and the assembly structure of the frame is complex. In addition, configurations of connectors or the like for connecting the elements of the frame to each other are complex. It takes a comparatively long time to assemble or disassemble the frame, and there is a need for separate tools. Furthermore, since the hard frame and the flexible hull are made of different materials, the coupling (integration) therebetween is incomplete. Moreover, portions of the hull to which water pressure is applied are curved toward the interior of the boat because the strength of the hull is lower than that of the frame. The curved portions increase frictional resistance to water, thus reducing the performance of the boat in water. Furthermore, the curved portions reduce the strength of the hull, so that the hull may be easily torn when it collides with a sharp rock or the like.
Techniques pertaining to a second category refer to inflatable boats, which are shaped by injection of air. A representative example pertaining to this category was proposed in U.S. Pat. No. 6,065,421 (title: INFLATABLE KAYAK, 2000) invented in common by Clayton Forbes Haller and Charles Prior Hall.
In this technique, the kayak can be markedly reduced in volume and length when it is stored. The basic weight of the kayak can be also reduced. Furthermore, the kayak is designed such that it is easy to inject or discharge air into or from the kayak body. However, since the external shape of the boat is formed by injecting air thereinto, it is difficult to make not only a bow part of the boat but also a stem part be sharp and streamlined. Thus, water resistance applied to the boat is increased, whereby the basic performance of the boat is reduced. Given this, studies on this technique are not actively being conducted.
Techniques pertaining to a second category refer to techniques of: assembling body panels with each other using fasteners to form a boat without using a separate frame for the boat; forming a boat body by means of folding one piece of panel with a film-shaped retainer used to retain the shape of the boat formed by folding the panel; or forming a boat by means of folding a single thin hard panel having a predetermined flexibility, i.e., a light and high-strength synthetic resin corrugated sheet, which will be described in detail later herein, in a similar manner to that of paper folding.
Techniques pertaining to this third category were proposed in U.S. Pat. No. 4,574,725 (title: COLLASIBLE BOAT, 1986) invented by Dennis Dowd, U.S. Pat. No. 4,706,597 (title: SEAMLESS FOLDABLE BOAT, 1987) invented by Frank M. Fl gone, U.S. Pat. No. 4,911,095 (title: COLLAPSIBLE BOAT WITH REMOVABLE TRANSOM PANEL, 1990) invented by Alex R. Kaye, U.S. Pat. No. 6,006,691 (title: KNOCK-DOWN BOAT ASSEMBLY, 1999) invented by Stephen E. Wilce, U.S. Pat. No. 6,615,762 (title: FOLDABLE BOAT WITH LIGHT WEIGHT HULL CONSTRUCTION SYSTEM, 2003) invented by Stephen E. Wilce, and U.S. Pat. No. 8,316,788 (title: COLLAPSIBLE KAYAK, 2012) invented by Anton Michael Willis.
Among the techniques pertaining to the third category, there is a need for US patent techniques of the last two cases to be described in more detail with regard to the foldable canoe according to the present invention.
First, the technique proposed in the technique of U.S. Pat. No. 6,615,762 has several significant technical characteristics different form the other conventional techniques in the foldable boat field. It is that the body of the boat is made of a thin corrugated sheet with a thickness ranging from 5 mm to 6 mm, i.e., marketed as brand name HI.about.CORE®COROPLAST™, COREX, PLASTICCORE®, BIPLEX, etc., formed by extruding ultralight thin hard material, that is, high-strength polyethylene, high-density plastic or the like without a reduction in formability, foldability, and strength. In detail, as shown in FIG. 27d, a resin corrugated sheet CS used in this technique is a corrugated sheet that includes: a pair of panels 56 which are arranged parallel to each other with a predetermined distance therebetween to form front and rear surfaces; and a plurality of spacers 57 that perpendicularly connect the panels 56 to each other. Such a synthetic resin corrugated sheet was already known in other industrial fields, for example, as being widely used as the material of a box for packing objects, e.g., a moving box. Although U.S. Pat. No. 6,615,762 does not includes the ultralight corrugated sheet itself used as the material of a boat in claims, it proposed use of the corrugated sheet as the material of a disassemblable boat based on the facts that the corrugated sheet is neither affected by water, nor corrodes or rusts, and is excellent in impact resistance, penetration resistance, and weatherproofness providing resistance to severe external environment conditions, etc.
As shown in FIGS. 27a through 27d, in this technique, the boat body includes a plurality of individual corrugated sheets CS1 that are designed in predetermined shapes, and each of which has several folding lines 50. When the boat is assembled, the corrugated sheets CS1 are appropriately folded along the folding lines 50 and are arranged. The corrugated sheets are thereafter coupled to each other by screws with annular ribs R interposed between the lateral opposite ends of the corrugated sheets, thus forming the body of the kayak boat as shown in FIG. 27a. Unlike the existing techniques, in the technique of U.S. Pat. No. 6,615,762, each folding line on which the corrugated sheet is folded functions as a living hinge such that even after the sheet is repeatedly folded and unfolded around the folding line, it is prevented from being broken off. Therefore, this technique does not require a separate hinge. Furthermore, physical processes for forming the corrugated sheet, i.e., cutting a predetermined unit panel, boring holes such as screw coupling holes having various sizes in the panel, and pressing the panel to form a folding line, can be conducted at the same time, for example, by a single pressing process. Consequently, this technique is evaluated as being able to markedly enhance the productivity.
With regard to use of a high-strength ultralight synthetic resin corrugated sheet as the material for foldable boats, the technique of U.S. Pat. No. 6,615,762 is known as being the first in the world. Furthermore, this technique provides secondary effects of facilitating printing on the outer surface of a hull of the boat.
Meanwhile, in the same manner as the technique of U.S. Pat. No. 6,615,762, the technique of U.S. Pat. No. 8,316,788 uses a synthetic resin corrugated sheet as the material for boat bodies and thus has the same technical effects resulting from use of the synthetic resin corrugated sheet. However, unlike the technique of U.S. Pat. No. 6,615,762 in which the boat body is formed by joining the several separated corrugated sheets with each other, a single synthetic resin corrugated sheet is used, and folding lines are formed on the sheet designed such that the sheet can be formed in a boat shape by folding the sheet along the folding lines. That is, the single synthetic resin corrugated sheet has only to be folded or unfolded in a similar manner to that of paper folding to form a boat or make it become a package form for storage.
Formed in the synthetic resin corrugated sheet, the folding lines of the technique of U.S. Pat. No. 8,316,788 also function as living hinges, which are not broken even after they are repeatedly bent along the folding lines. Because the single corrugated sheet is used to form a boat body, this technique has not only the effects of the technique of U.S. Pat. No. 6,615,762 but also effects of a reduction in the number of elements and facilitation of assembly and disassembly processes.
However, the crucial point to note is that both the techniques of U.S. Pat. Nos. 6,615,762 and 8,316,788 pertain to kayaks rather than canoes. Although kayaks and canoes are similar in that both are personal non-powered small boats, it should be noted that there is a great difference in mechanical structure therebetween.
In more detail, kayaks are configured such that a side bottom panel that is immersed in water and brought into contact with water is integrally connected to an upper deck that substantially horizontally covers the upper ends of left and right side panels and does not come into contact with water. A tubular closed space defined by the side bottom panel and the upper deck becomes a cockpit in which a user sits. Generally, a coaming or the like is provided for preventing water from entering the cockpit through an opening of the cockpit, which is formed in an approximately central portion of the upper deck.
Unlike such kayaks, canoes typically have an open top boat structure, and have a non-tubular shape, including only a side bottom panel without a separate upper deck.
To make a boat manufactured by shaping a thin planar sheet using a given amount of material (to form a predetermined cross-sectional area and surface area) have a mechanically stable structure strong enough to resist to external force, the boat must be shaped such that the section performance thereof (particularly, geometrical moment of inertia) are increased. With regard to manufacture of a boat using a thin synthetic resin corrugated sheet, in the case of kayaks having a closed tubular body structure, the geometrical moment of inertia is comparatively large so that the resistance to external force can be easily increased. However, in the case of canoes generally having an open top structure, the geometrical moment of inertia thereof is smaller than that of the kayaks. Thus, it is not easy to manufacture an open top canoe by means of folding a thin sheet. As the result of tests, for example, if an open top canoe having a length ranging from 3 m to 4 m and a central width of about 1 m is formed by folding a thin synthetic resin corrugated sheet, the shape of a boat is not satisfactorily formed or it is difficult to retain the shape of a side panel moving limply because the section performance as a canoe boat is very low although the physical (mechanical) properties, such as strength, durability, etc., of the synthetic resin corrugated sheet are excellent.
Due to these reasons, both the inventor of U.S. Pat. No. 6,615,762 and the inventor of U.S. Pat. No. 8,316,788 would have thought that kayaks having a longitudinal tubular body structure are easier to manufacture using a light and thin synthetic resin corrugated sheet having a high strength. This aspect can be easily verified in that: in U.S. Pat. No. 6,615,762, a tubular structure is formed by enclosing the circumferences of the annular ribs with panels forming the boat body; in U.S. Pat. No. 8,316,788, claim 1 includes, as an essential configuration, forming a tubular shape by folding left and right panels along a longitudinal axis and joining opposite edges of left and right panels to each other; and another independent claim 22 includes, as an essential configurations integrally forming the keel of the kayak (keel: a long and large member provided parallel to a center axis on the bottom of a boat so as to support the hull of the boat), the hull (the side bottom panel), and the deck (the upper cover panel).
Therefore, there is a need for a technique that can construct a body of a boat by folding a single high-strength thin synthetic resin sheet in a similar manner to that of paper folding, and that can construct an open top (deckless) boat, i.e., a canoe, having a mechanically stable structure without the side bottom panel moving limply. The present invention is provided to satisfy this need.